1. Field of the Invention
An aspect of the present invention is directed to handover in a wireless LAN environment. More particularly, an aspect of the present invention relates to a method for providing information as to whether media independent handover (MIH) services as defined by the Institute of Electrical and Electronics Engineers (IEEE) 802.21 specification are available for use in a network to which a mobile node belongs, and an access point performing the method.
2. Description of the Related Art
A rapid increase of users of mobile communication services has led to activation of mobile communication services supporting multimedia communications, and seamless communication services have been requested by mobile users. Accordingly, it has become important to achieve a fast handover in the wireless LAN environment based on the IEEE 802.11 specification.
FIG. 1 illustrates a conventional wireless LAN environment.
Referring to FIG. 1, the wireless LAN environment includes a mobile node (MN) 1, an access point (AP) A 10, an access point B 20, an access point C 30, an access point D 40, an access router (AR) A 50 and an access router B 60.
The mobile node 1, which can be a mobile phone, a personal digital assistant (PDA), or a notebook computer, moves between several wireless LANs. Each of the access points A, B, C and D 10, 20, 30 and 40 connects the mobile node 1 to a subnet to which the mobile node 1 belongs, thereby allowing the mobile node 1 to access a wired network like the Internet. Hereinafter, a device performing this role will be called an “access point.”
The access routers A and B 50 and 60 provide the mobile node 1 with routing services in a subnet to which each of them belongs, thereby allowing the mobile node 1 to access an arbitrary node in the subnet using an optimal path.
As illustrated in FIG. 1, the conventional wireless LAN environment will be described under the assumption that the mobile node 1 passes through a basic service set (BSS) managed by the access point A 10, a BSS managed by the access point B 20, a BSS managed by the access point C 30 and a BSS managed by the access point D 40 in sequence. BSS is a term used in the IEEE 802.11 specification, and it refers to a wireless LAN managed by a single access point.
In order to allow the moving mobile node 1 to know which access point to use for accessing a wired network, each of the access points A, B, C and D 10, 20, 30 and 40 periodically transmits a beacon signal that indicates its managed BSS.
In communications denoted by 11 in FIG. 1, the mobile node 1 receives a beacon signal from the access point A 10. Based on the received beacon signal, the mobile node 1 becomes aware that it is positioned in the BSS managed by the access point A. The mobile node 1 accesses a wired network by way of the access point A 10, as it did previously.
In communications denoted by 21 in FIG. 1, the mobile node 1 receives a beacon signal from the access point B 20. Based on the received beacon signal, the mobile node 1 becomes aware that the BSS in which it is positioned has changed. Accordingly, the mobile node 1 conducts a handover due to the change of the BSS, i.e., handover in a link layer. That is, the mobile node 1 becomes aware that it is positioned in the BSS managed by the access point B 20, and changes its link layer connection with the access point A 10 to a link layer connection with the access point B 20. Referring to the open systems interconnection (OSI) reference model, since the link layer corresponds to a second layer, the handover in the link layer is called a handover in the second layer or an L2 handover for short.
The mobile node 1 accesses a wired network by way of its new access point B 20.
In the communications denoted by 22 in FIG. 1, the mobile node 1 transmits a router solicitation for proxy advertisement (RtSolPr) frame including information that the BSS in which it is positioned has changed, to the access router A 50 by way of the access point B 20. The access router A 50, which has not received the information through any other access router, becomes aware that the mobile node 1 is positioned within its subnet.
In the communications denoted by 23 in FIG. 1, the access router A 50 transmits a proxy router advertisement (PrRtAdv) frame, including information that the subnet has not changed, to the mobile node 1 by way of the access point B 20. The mobile node 1 that receives this frame becomes aware that it is positioned within the subnet managed by the access router A 50. Accordingly, the mobile node 1 does not conduct a handover, i.e., handover in an Internet protocol (IP) layer. Referring to the OSI reference model, since the IP layer corresponds to a third layer, handover in the IP layer is called a handover in the third layer or an L3 handover for short.
In the communications denoted by 24 in FIG. 1, the mobile node 1 receives a beacon signal from the access point B 20. Based on the received beacon signal, the mobile node 1 becomes aware that it is positioned within the BSS managed by the access point B 20. The mobile node 1 accesses a wired network by way of the access point B 20, as it did previously.
In the communications denoted by 31 in FIG. 1, the mobile node 1 receives a beacon signal from the access point C 30. Based on the received beacon signal, the mobile node 1 becomes aware that the BSS in which it is positioned has changed. Accordingly, the mobile node 1 conducts handover due to the change of the BSS, i.e., handover in a link layer. That is, the mobile node 1 becomes aware that it is positioned in the BSS managed by the access point C 30, and changes the link layer connection with the access point 10 A to a link layer connection with the access point C 30. The mobile node 1 accesses a wired network by way of its new access point C 30.
In the communications denoted by 32 in FIG. 1, the mobile node 1 transmits an RtSolPr frame, including information that the BSS in which it is positioned has changed, to the access router A 50 by way of the access point C 30 and the access router B 60. The access router A 50 that receives this information by way of the access router B 60, which is a different access router, becomes aware that the mobile node 1 is not in its subnet.
In the communications denoted by 33 in FIG. 1, the access router A 50 transmits a PrRtAdv frame, including information that the subnet in which the mobile node 1 is positioned has changed, to the mobile node 1 by way of the access router B 60 and the access point C 30. The mobile node 1 that receives this frame becomes aware that the subnet in which it is positioned has changed. Accordingly, the mobile node 1 conducts handover due to the change of the subnet, i.e., handover in an Internet protocol (IP) layer.
In the communications denoted by 41 in FIG. 1, the mobile node 1 receives a beacon signal from the access point D 40. Based on the received beacon signal, the mobile node 1 becomes aware that the BSS in which it is positioned has changed. Accordingly, the mobile node 1 conducts handover due to the change of the BSS, i.e., handover in the link layer. The mobile node 1 becomes aware that it is positioned within the BSS managed by the access point D 40, and changes the link layer connection with the access point C 30 to a link layer connection with the access point D 40. The mobile node 1 accesses a wired network by way of its new access point D 40.
In the communications denoted by 42 in FIG. 1, the mobile node 1 transmits an RtSolPr frame, including information that the BSS in which it is positioned has changed, to the access router B 60 by way of the access point D 40. The access router B 60 that receives this frame (not through any other access router) becomes aware that the mobile node 1 is positioned within its subnet.
In the communications denoted by 43 in FIG. 1, the access router B 60 transmits a PrRtAdv frame, including information that the subnet has not changed, to the mobile node 1 by way of the access point D 40. The mobile node 1 that receives this frame becomes aware that it is positioned within the subnet managed by the access router B 60. Accordingly, the mobile node 1 does not conduct handover due to the change of the subnet, i.e., handover in the IP layer.
As described above, a mobile node communicates with an access router to obtain information of a change of a subnet that it accesses, since it does not know whether the subnet has changed. In other words, the mobile node communicates with the access router in order to determine whether to conduct the handover only in the link layer, or the handovers both in the link layer and the IP layer.
Handover due to movement of a mobile node between homogeneous networks is illustrated in FIG. 1. However, research to support seamless mobility between heterogeneous networks is being conducted.
Especially, wireless technology recently gathering strength as a main art is classified into WLAN (the IEEE 802.11 standard) and cellular. To support mobility between these wireless networks, organizations participating in wireless standardization, including IEEE 802, 3GPP, 3GPP2, ITU-T and IETF, are actively focusing on solving known problems.
Among them, the research on IEEE 802 is the most active, especially, IEEE 802.21 WG and IEEE 802.11 WIEN SG.
IEEE 802.21 WG is focused on standardization to provide media independent solutions for mobility between heterogeneous networks. In particular, it created a new layer 2.5 model between a MAC layer and its upper IP layer, thereby making it possible to support efficient mobility in various wired and wireless environments.
For this, the working group of IEEE 802.21 has been in discussion about a method for realizing a media independent handover (MIH) protocol. In connection with this, the content disclosed in: www.ieee802.org/21 may be referenced.
Even when a mobile node, operating according to the MIH protocol, moves to a heterogeneous network, the mobile node can conduct continuous communication since handover is possible when an access point in the target heterogeneous network supports the MIH protocol.
However, when the mobile node does not support the MIH protocol or when it supports the MIH protocol but the access point in the target heterogeneous network does not support the MIH protocol, handover cannot be conducted.
Accordingly, there is a need for the mobile node to know whether the access point in the target heterogeneous network supports the MIH protocol.